The matter disclosed herein relates to electrical generators and, in particular, to a generator arrangement in which the functionality of two typically separate electrical power generators are combined together into a single generator that comprises part of a three-in-one combined multi-generator which has a dual drive path with a shear section that immunizes one of the generators (e.g., the permanent magnet generator) within the single combined multi-generator from a failure of another generator (e.g., the main generator) within the single combined multi-generator.
Modern aircraft engines are typically controlled electronically. It is a known practice to power an electronic engine control (“EEC”) by a dedicated permanent magnet generator (“PMG”) that is driven independently by a drive pad on an accessory gearbox. Another pad on the same gearbox drives another generator that could be used for main or any other category of power. However, to save an accessory drive pad, it is desired to combine, on a single drive pad or power take-off (“PTO”), the EEC PMG with the PMG that is internal to and is commonly part of a brushless, three-in-one multi-generator that also includes a main generator which is typically used for aircraft applications such as providing electrical power for the deicing function on the aircraft. At the same time, to achieve hyper reliability in the single combined multi-generator, and an even higher reliability in the EEC PMG, it is desired to make the EEC PMG immune from a mechanical failure of the main or deicing generator.
Known configurations exist in the prior art for providing an electrical generator with a mechanical failure (e.g., overload) capability. In one such configuration an electrical generator has a coaxial or concentric drive shaft system that is provided with an overload shearable coupling for driving multiple outputs from a single input. A pair of coaxial, concentric telescoped drive shafts are provided as independent outputs to a pair of corresponding driven devices, such as a blower and a rotor of a generator. A singular input shaft is coupled to the pair of drive shafts by a gearbox for simultaneously rotating the coaxial drive shafts. A shear section is formed in one of the drive shafts (e.g., the outer drive shaft) for rupturing or breaking the outer drive shaft in response to an overload, mechanical failure condition thereon, while the other coaxial, inner telescoped drive shaft continues to be rotated by the singular input shaft despite the failure of the outer drive shaft.
However, this known dual coaxial or concentric drive shaft configuration has some inherent drawbacks in that the strength of the shear section formed in the outer drive shaft can be relatively too great to adequately protect the gearbox. This is because the outer drive shaft has to accommodate the inner drive shaft which itself needs to be of a certain size. Thus, in this configuration the inner diameter of the outer drive shaft is limited by the maximum outer diameter of the inner drive shaft. Also, in this known, dual coaxial drive shaft configuration the outer drive shaft (i.e., the “stub” shaft) is largely unsupported except on the splines and the “O” rings, leaving the outer drive shaft inherently unstable. Yet, the outer drive shaft, while being inherently unstable, nevertheless is attempting to support the inner drive shaft. Therefore, what is needed is an improvement to this known dual coaxial or concentric drive shaft configuration.